Blanch the leaves in plenty of boiling salted water. Drain then leave it to soak in cold water for 2 hours.
Bring the broth to the boil with the carrots, 2 of the onions, the celery and parsley, simmer until they are cooked. Fry the pork fat with the remaining onion.
Drain the leaves and squeeze them out between your hands to get rid of all the water. Chop and add to the pan.